<form id="form1" runat="serve"  >
    <div>
  <fieldset class="form-iscrizione">
    <h2>Iscrizione newsletter</h2>

    <label>La tua email: <input name="email" type="text"></label>
    <input type="hidden" name="list" value="2">
    <input type="hidden" name="group" value="27">
<%--      <asp:Button runat="server" ID="Iscriviti" Text="Iscriviti"  />--%>
    <input name="Submit" type="Submit" onClick="return isEmail(document.myForm.email.value);" value="Iscriviti">
  </fieldset>

    </div>
    </form>